U.S. patent application number 17/550086 was filed with the patent office on 2022-04-07 for insulation film.
The applicant listed for this patent is WHIRLPOOL CORPORATION. Invention is credited to ERMANNO BUZZI, MUHAMMAD KHIZAR.
Application Number | 20220107090 17/550086 |
Document ID | / |
Family ID | |
Filed Date | 2022-04-07 |
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United States Patent
Application |
20220107090 |
Kind Code |
A1 |
KHIZAR; MUHAMMAD ; et
al. |
April 7, 2022 |
INSULATION FILM
Abstract
Aspects of the disclosure generally relate to an insulation
film, including a thermal insulation film or an insulation film for
a cooking appliance. The insulation film can include a substrate, a
first layer comprising silver nanowires proximate to the substrate,
and a second layer comprising porous alumina proximate to the first
layer and distal from the substrate.
Inventors: |
KHIZAR; MUHAMMAD; (SAINT
JOSEPH, MI) ; BUZZI; ERMANNO; (VARESE, IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WHIRLPOOL CORPORATION |
BENTON HARBOR |
MI |
US |
|
|
Appl. No.: |
17/550086 |
Filed: |
December 14, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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16242069 |
Jan 8, 2019 |
11236912 |
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17550086 |
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International
Class: |
F24C 15/04 20060101
F24C015/04; B32B 7/12 20060101 B32B007/12; B32B 9/04 20060101
B32B009/04 |
Claims
1. An insulation film for a cooking appliance, comprising: a
substrate; a first layer comprising silver nanowires proximate to
the substrate; and a second layer comprising porous alumina
proximate to the first layer and distal from the substrate, with
the porous alumina having an average pore size of 10-35
micrometers.
2. The insulation film of claim 1, wherein the silver nanowires
have a diameter of 10-20 micrometers.
3. The insulation film of claim 2, wherein the silver nanowires
have a spacing of 150-200 nanometers.
4. The insulation film of claim 3, wherein the silver nanowires
have an area density of 0.15-0.25 g/m.sup.2.
5. The insulation film of claim 1, wherein the first layer
comprises a first layer thickness of 50-100 micrometers.
6. The insulation film of claim 5, wherein the second layer
comprises a second layer thickness of 50-100 micrometers.
7. The insulation film of claim 6, further comprising an overall
thickness defined by the first layer thickness, the second layer
thickness, and a substrate thickness of the substrate, wherein the
overall thickness is between 200-250 micrometers.
8. The insulation film of claim 1, wherein the substrate comprises
an adhesive.
9. The insulation film of claim 1, wherein the first layer further
comprises a polymeric material with the silver nanowires dispersed
within the polymeric material.
10. The insulation film of claim 1, wherein the silver nanowires
form at least one of a structured mesh or an unstructured mesh.
11. The insulation film of claim 2, further comprising additional
silver nanowires dispersed within the second layer.
12. The insulation film of claim 11, wherein the additional silver
nanowires have a diameter of 10-20 nanometers.
13. The insulation film of claim 12, wherein the additional silver
nanowires have a length of 10-80 micrometers.
14. The insulation film of claim 13, wherein the additional silver
nanowires have an average spacing of 150-200 nanometers.
15. The insulation film of claim 1, wherein the first layer further
comprises porous alumina silicate.
16. A thermal insulation film, comprising: a first layer comprising
a mesh of silver nanowires with a diameter of 10-20 micrometers and
an area density of 0.15-0.25 g/m.sup.2; and a second layer abutting
the first layer and comprising porous alumina with an average pore
size of 10-35 micrometers; wherein an emissivity of the first layer
is between 0.02-0.8.
17. The thermal insulation film of claim 16, further comprising an
adhesive substrate coupled to the first layer.
18. The thermal insulation film of claim 16, further comprising
additional silver nanowires dispersed within the second layer.
19. The thermal insulation film of claim 18, wherein the additional
silver nanowires have at least one of a diameter of 10-20
nanometers, a length of 10-80 micrometers, or an average spacing of
150-200 nanometers.
20. The thermal insulation film of claim 16, wherein the first
layer comprises a first layer thickness between 50-100 micrometers,
and wherein the second layer comprises a second layer thickness
between 50-100 micrometers.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 16/242,069, filed Jan. 8, 2019, now allowed,
which is incorporated herein by reference in its entirety.
BACKGROUND
[0002] Cooking appliances typically include a heated chamber for
cooking a food item, and one or more components responsible for the
mechanical or electrical operations of the appliance. For example,
an oven can include a hinged door with a handle, or a
user-interface component such as a knob or a control pad for a user
to direct operation of the oven. Components of the oven can include
a heat-resistant property to provide for user interaction with such
components during heating of the chamber.
BRIEF DESCRIPTION
[0003] In one aspect, the disclosure relates to an insulation film
for a cooking appliance including a substrate, a first layer
comprising silver nanowires proximate to the substrate, and a
second layer comprising porous alumina proximate to the first layer
and distal from the substrate, with the porous alumina having an
average pore size of 10-35 micrometers.
[0004] In another aspect, the disclosure relates to a thermal
insulation film including a first layer comprising a mesh of silver
nanowires with a diameter of 10-20 micrometers and an area density
of 0.15-0.25 g/m2, and a second layer abutting the first layer and
comprising porous alumina with an average pore size of 10-35
micrometers, wherein an emissivity of the first layer is between
0.02-0.8.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] In the drawings:
[0006] FIG. 1 is a schematic perspective view of an exemplary
household cooking appliance according to various aspects described
herein.
[0007] FIG. 2 is a side sectional view of the household cooking
appliance of FIG. 1 along line II-II including a component in the
form of a handle.
[0008] FIG. 3 is a schematic view of an insulation film that can be
utilized in the component of FIG. 2 with layers and heat flows
illustrated.
[0009] FIG. 4 is a schematic side view of another component for the
household cooking appliance of FIG. 1 in the form of a knob that
can include the insulation film of FIG. 3.
[0010] FIG. 5 is a flowchart illustrating a method of forming the
insulation film of FIG. 3.
DETAILED DESCRIPTION
[0011] Aspects of the disclosure relate to a heat-resistant
component in the form of an insulation film containing nanowires.
Aspects of the disclosure are described in the context of a
household cooking appliance, such as an oven. It will be understood
that the disclosure is not so limited and can have general
applicability, including to any component in a heated
environment.
[0012] Some cooking appliances or other heat-generating appliances
can include pocket-style handles wherein a user pulls on a recessed
portion of a door or access panel adjacent a heated chamber. During
operation of the appliance, heat can localize or be trapped within
the recessed portion of the pocket handle. This can cause an
undesirably high temperature within the recessed portion or on
surfaces of the handle that a user might grasp.
[0013] FIG. 1 illustrates an exemplary household cooking appliance
10 in the form of an oven. It will be understood that while
illustrated as an oven, the household appliance can include any
home appliance used for cooking or preparing food, including a
toaster oven or cooktop in non-limiting examples.
[0014] The cooking appliance 10 can include a cabinet 12 with an
open-faced cooking chamber 14 defined by a pair of spaced side
walls 16, 18 joined by a top wall 20, a bottom wall 21, and a rear
wall 23. A door 24 selectively closes the chamber 14. The door 24
in an open position can allow a user to access the chamber 14,
while the door 24 in a closed position prevents access to the
chamber 14 and seals the chamber 14 from the external environment.
A handle 26 can be provided in the door 24 for moving the door 24
between open and closed positions.
[0015] The cooking appliance 10 can also include at least one
heating element 30, which is illustrated in the example of FIG. 1
as being hidden or mounted beneath the cooking chamber bottom wall
22 in a heating element housing 32. Heat from the heating element
30 can conduct through the bottom wall 22 and into the chamber 14.
Alternatively, the heating element 30 can be mounted inside the
chamber 14, where heat can conduct or radiate inside the chamber
14, such as along the side walls 16, 18 in non-limiting examples.
While not shown, a convection fan can also be provided in the
cooking appliance 10 for circulating air or steam within the
chamber 14. A food item 35 can be placed within the chamber 14 to
be cooked by the cooking appliance 10.
[0016] A human-machine interface or user interface 40 can also be
provided in the cooking appliance 10. The user interface 40 can
include any suitable interface for input or control of the cooking
appliance 10, such as an electronic display or touchscreen display,
as well as manually-operated components such as buttons, dials, or
switches. In the illustrated example, the user interface 40
includes a knob 42 and an electronic panel 44 provided in a front
wall 21 of the cabinet 12. The electronic panel 44 can include at
least one electronically-controlled switch (not shown). It will be
understood that the user interface 40 can include more or fewer
components than those shown.
[0017] Turning to FIG. 2, a side sectional view of the cooking
appliance 10 is illustrated. The door 24 can include a door body 50
with an inner surface 51 thermally confronting the cooking chamber
14 and an outer surface 52 within which the handle 26 can be
located. As used herein, a surface "thermally confronting" the
cooking chamber 14 will refer to a surface being thermally coupled
to the cooking chamber 14 such that heat within the cooking chamber
14 can be transferred to the surface, including by conduction,
convection, or radiation.
[0018] In the illustrated example, the handle 26 is in the form of
a "pocket." More specifically, the handle 26 can include a handle
body 54 with an inner contact surface 55 thermally confronting the
cooking chamber 14, as well as an outer handle surface 56 that is
flush or coplanar with the door outer surface 52. A gap 57 can be
defined between the inner contact surface 55 and outer handle
surface 56. A user can insert a hand into the gap 57 and pull on
the inner contact surface 55 to open the door 24. In an alternate
example (not shown), the handle can be in the form of a bar
projecting outward from the door 24, wherein a user can grasp the
bar and pull to open the door 24.
[0019] A composite 70 can be disposed on the inner contact surface
55. The composite 70 can be in the form of an insulation film 76
and include a first layer 71 and a second layer 72. The composite
70 can be utilized to prevent excessive heating of the handle 26
during operation of the cooking appliance 10. Optionally, the
composite 70 can also be applied to other surfaces of the door 24,
such as the inner surface 51 or the outer surface 52.
[0020] Turning to FIG. 3, the composite 70 is illustrated in
further detail. The first layer 71 of the composite 70 can include
silver nanowires 73 forming a mesh. In one example the mesh can be
a structured fiber mesh, such as a woven fiber mesh with at least
one ply. In another example the mesh can be a non-structured mesh
wherein the fibers have random orientations within the mesh. The
second layer 72 of the composite 70 can include porous alumina 74
with air-filled pores 78 defined within the second layer 72. For
clarity, some exemplary pores 78 are illustrated and it should be
understood that the pores 78 can be arranged throughout the second
layer 72, including with an ordered or random orientation within
the second layer 72. In the illustrated example, the first layer 71
is proximate the inner contact surface 55 of the handle 26, and
lies between the inner contact surface 55 and the second layer
72.
[0021] Optionally, a substrate 75 having a substrate thickness 77
can be included in the composite 70. In one example, the substrate
75 can include an adhesive and can be positioned between the inner
contact surface 55 and first layer 71. The first layer 71 can be
proximate to the substrate 75, and the second layer 72 can be
proximate to the first layer 71 and distal from the substrate 75.
It is contemplated that the first and second layers 71, 72 and
substrate 75 can at least partially define the insulation film 76,
and can be applied to the inner contact surface 55 of the handle 26
in one non-limiting example.
[0022] The first layer 71 can be formed of a polymeric material
with the silver nanowires 73 dispersed within the polymeric
material. The first layer 71 can have a first layer thickness 81
and an area density 82. The silver nanowires 73 can have a diameter
83 and a length 84. An average spacing 85 can be defined between
adjacent silver nanowires 73. In one non-limiting example, the
diameter 83 can be approximately 10-20 nm, including 15-17 nm, the
average spacing 85 can be approximately 150-200 nm, the length 84
can be approximately 10-80 .mu.m, the first layer thickness 81 can
be approximately 50-100 .mu.m, and the area density can be
0.15-0.25 g/m.sup.2. As used herein, "approximate" or
"approximately" will refer to a value that does not differ from a
stated numerical value (e.g. 0.2 g/m.sup.2) or from a range of
numerical values (e.g. 100-400 nm) by more than a predetermined
limit. In one example the predetermined limit can be relative, such
within 10% of a stated numerical value or a range of numerical
values. In another example the predetermined limit can be an
absolute limit, such as 1 micrometer or smaller. In still another
example the predetermined limit can be based on another parameter,
such as the average spacing 85 not being more than 10 times the
diameter 83 of the silver nanowires 73.
[0023] The second layer 72 can have a second layer thickness 91,
such as between 50-100 .mu.m in a non-limiting example. An average
pore size 92 of the porous alumina structure can be defined within
the second layer 72, such as approximately 10-35 .mu.m, or
22.9.+-.10.3 .mu.m in non-limiting examples. It is contemplated
that the composite 70 can have an overall thickness 93 at least
partially defined by the first and second layer thicknesses 81, 91,
and substrate thickness 77. In one non-limiting example, the
overall thickness 93 can be 200-250 .mu.m. Silver nanowires 73 can
also be provided within the second layer 72, including with an
exemplary diameter 83 of approximately 10-20 nm, a length 84 of
approximately 10-80 .mu.m, and an average spacing 85 of
approximately 150-200 nm in one non-limiting example.
[0024] Arrows illustrate heat transfer during operation of the
cooking appliance 10 (FIG. 1). Heat shown with arrows 100 from
within the cooking chamber 14 can flow toward the first layer 71.
The mesh of silver nanowires 73 can reflect a portion of the heat,
shown by arrow 101, back into the cooking chamber 14. Remaining
heat can flow toward the second layer 71. The silver nanowires 73
within the second layer 72 can reflect a portion of the incoming
heat, shown by arrow 102, back toward the cooking chamber 14. In
addition, the air-filled pores 78 formed within the porous alumina
74 can block another portion of the incoming heat, shown by arrow
103, from transferring through the second layer 72. A very small
fraction of heat, shown by arrow 104, can transfer through the
second layer 72. In this manner, the insulation film 76 can both
reflect or "reject" heat from entering a layer 71, 72, as well as
insulate or "block" heat from transferring through a layer 71,
72.
[0025] Referring now to FIG. 4, another component that can be
utilized in the cooking appliance 10 is shown in the form of the
knob 42 projecting from the front wall 21. The knob 42 can include
a knob body 60 with an inner surface 62 thermally confronting the
chamber 14 (FIG. 2), as well as a rotatable portion 64 connected to
the inner surface 62 by a shaft 66. A user can grasp the rotatable
portion 64 to operate the knob 42, such as to adjust a temperature
setting of the cooking chamber 14.
[0026] Insulation film 76 can also be disposed on the inner surface
62 of the knob 42, such as to prevent excessive heating of the knob
42 during operation of the cooking appliance 10. In one example,
the insulation film 76 can be applied to the knob 42 after
manufacture of the knob 42, such as by an adhesive or other
coupling mechanism. In another example, the knob 42 can be formed
integrally with the insulation film 76, such as by placing
insulation film 76 into an injection mold prior to forming the knob
42. In such a case, the inner surface 62 of the knob 42 can be
injection molded with the insulation film 76 already in place. In
the illustrated example, the insulation film 76 is positioned
between the inner surface 62 and the front wall 21, with the first
layer 71 proximate the inner surface 62 and the second layer 72
proximate the first layer 71.
[0027] Turning to FIG. 5, one exemplary method 110 is described for
forming silver nanowires 73 that can be utilized in the insulation
film 76. It will be understood that the method described below
provides one example of forming the silver nanowires 73. The method
110 can include other aspects not explicitly described, and that
aspects of the method 110 can be performed in any suitable
order.
[0028] The method 110 can optionally include precursor heating at
112 which can be utilized to grow silver nanowires 73. For example,
a solution containing silver nitrate can be heated to a suitable
reaction temperature. In one example, silver nanowires with a
diameter of 17.+-.2 nm can be obtained at an injection rate of 2.5
mL/s and a reaction temperature of 100.degree. C. The silver
nanowires can have uniform diameters, and lengths varying from
approximately 10 microns to approximately 40 microns. Optionally,
the silver nanowires can be dispersed into a solvent such as
ethanol or ethylene glycol in non-limiting examples. Other
surfactants can also be added such as two-system-based
pre-polymerized polymer (1:10 ratio). In one example,
pre-polymerized liquid silicon can be utilized. One benefit of
using such a liquid silicon is that it can cure rapidly at elevated
temperatures. In one example, a 2.5 mm cross-section can cure
within approximately 10-15 seconds at 200.degree. C. In this
manner, a blending matrix can be developed utilizing a
pre-polymerized polymer as a blending agent with silver nanowires
73. Unique about this technique is its dispersion performance which
is prepared as secondary dispersions or by polyaddition of
pre-polymers in aqueous systems. The dispersion process can also be
adjusted or tailored based on, in non-limiting examples, solubility
or insolubility of monomer and initiator, respectively, the
presence or absence of surfactant, droplet sizes, particle sizes,
or particle formation mechanisms.
[0029] In one non-limiting example of reaction conditions utilizing
ethylene, an ethylene pressure of 10 to 40 atm and temperature of
30.degree. C. to 75.degree. C. can be utilized, wherein the
ethylene does not form a separate liquid phase under these
conditions. The particle sizes (average) of the dispersions
obtained can be in the range from 100 to 200 nm. In one example,
during formation of a polymer dispersion a sufficiently large
number of primary particles were nucleated such that the final
particles was sufficiently small to be colloidally stable. A matrix
comprises of porous alumina silicate blended with 2-system based
pre-polymerized polymer can be prepared separately. It can be
appreciated that liquid polymer can be utilized to avoid the
overheating of the polymer particle when blended in pelletized
form. The use of liquid polymer can also help to reduce particle
overheating and agglomeration as well as control particle
morphology.
[0030] Exemplary polymers that can be utilized include, in
non-limiting examples, polymers and copolymers of acrylic and
methacrylic acids and esters, acrylonitrile, and acrylamide. Due to
their large polymerization shrinkage, it can be advantageous to
carry out their polymerization in stages to control the product
dimensions for use in large-surface-area nanomaterials such as
silver nanowires. For this, a two-system-based pre-polymerized
polymer can be used to prepare a mixture of polymer. Such a
pre-polymerized polymer can provide for ease of handling and
minimizes abrupt polymerization shrinkage by the use of
pre-polymerized powder. The pre-polymerized powder provides for
several benefits including no post-curing, excellent electrical
insulating properties, easily pigmented, superior unprimed adhesion
to glass fabric and extremely suitable for spray-on and dip coating
applications.
[0031] The pre-polymerized polymer can be mixed in two parts A and
B in a 10:1 ratio. Meter mix equipment can be utilized to pump and
mix the two components without excessive incorporation of air into
the mixture. In order to avoid air bubble entrapment during their
mixing process, the mixture can be thoroughly de-gassed under
vacuum to avoid the build-up of voids which may eventually effect
the overall thermal performance of the insulation film, especially
when used as a blending agent.
[0032] At 114, the first layer 71 of silver nanowires can be
applied to the substrate 75. The silver nanowires 73 can be applied
by spray deposition, including a spray-on coating technique wherein
the silver nanowires 73 are dispersed within pre-polymerized
polymer as described above. Optionally, the first layer 71 can be
pressed onto the substrate, such as via rollers or other
mechanisms.
[0033] At 116, the second layer 72 of porous alumina 74 can be
applied to the first layer 712. Optionally, the second layer 72 can
be pressed onto the first layer 71. The porous alumina 74 can, in
one example, include porous alumina silicate formed from kaolinite
and bentonite clay powders (natural colloidal, hydrated aluminum
silicates) mixed together along with active additives which can be
based on magnesium nitrate or aluminum nitrate. The porous alumina
silicate can be sintered at very high temperatures (e.g.
1800.degree. C.) to develop a porous ceramic structure with
selective microcrystalline and amorphous grain boundaries having
energy-efficient thermal insulation properties. The desired fine
pores (voids) can be formed by sintering raw ceramic powders at a
nondensifying temperature. A high porosity level can be achieved
via the addition of large quantities of pore formers such as resin
beads and carbon, which can be removed latter through oxidation
process.
[0034] In one example, the porous alumina ceramic can include
silica particles with diameters of about 10 nm to about 15 nm
developed by a slip casting technique, wherein an aqueous alumina
slurry is used with a control loading concentration of metallic
aluminum powder. Porosity of the used base material can aid in
chemical reaction of aluminum with water by hydrogen gas evolution
reaction and solidification of suspension at a temperature of
1650-1750.degree. C. The pore size distribution and mechanical
strength the porous alumina 74 can depend on the grain size of the
starting materials.
[0035] It can be appreciated that the insulation film 76 can be
utilized in a variety of contexts where thermal insulation
properties may be desired, including cooking appliance components
such as front panels, doors, door handles including pocket-style
handles, knobs, other fascia components, and other related
applications.
[0036] Aspects of the disclosure provide for several benefits,
including that the use of silver nanowires to form a conductive
porous network provides for increased reflection of heat, which can
reduce the amount of heat able to transfer to the outer surface.
For example, during operation of the oven, heat from within the
cooking chamber can transfer to outer components of the oven such
as a handle or other human-machine interface components such as
knobs, switches, touch panels, or the like. It can be appreciated
that the insulation film described herein can reduce an amount of
heat transfer to components that a user may touch, improving
operability of such user interface components.
[0037] In addition, improved chemical stability of silver nanowires
make these a suitable material for use as an active ingredient for
the proposed heat rejection technology. Silver nanowire meshes can
provide for highly effective trapping of thermal radiation,
including a high reflectance of thermal radiation from a wide range
of incidence angles, such as from approximately 0.degree.
(normal/perpendicular incidence) to approximately 85.degree. in a
non-limiting example. The insulating film described herein can have
significantly improved thermal insulation performance compared to
traditional heat reduction components, including a thermal
conductivity of approximately 2 W/m-K and a coefficient of thermal
expansion of approximately 3.6 .mu.m/m-.degree. C. for temperatures
ranging from approximately 25.degree. C. through 1000.degree.
C.
[0038] Another benefit is that the overall emissivity of the layer
having a mesh of silver nanowires is comparable to that of porous
alumina (approximately 0.80), which is much greater than the
emissivity of bulk silver (approximately 0.02) which provides for
excellent insulation against radiative heat loss from the
chamber.
[0039] In addition, as silver forms only a small fraction of the
overall mass of its layer, the insulation film described above
provides for a cost-effective solution with excellent insulating
properties. Spray-coating a silver nanowire solution can adds a
nominal area density of approximately 0.15 g/m.sup.2. Aspects of
the silver nanowires and layered structures described herein can
reflect heat, e.g. infrared radiation, by more than 90% back toward
the original heat source and the reported increase in its heat
reflectance is due to differences in the materials' emissivity.
Low-emissivity materials like silver, which has an emissivity of
0.02, emit less radiation and can provide much better insulation
than other high-emissivity materials. Silver nanowires with lengths
and spacing distances as described herein can improve film packing
and stacking options for forming the insulated film. In addition,
the proposed spray coating deposition process provides for a
low-cost technique that reduces manufacturing time as well as
provides for repeatable populating of silver nanowires within the
layers as described.
[0040] To the extent not already described, the different features
and structures of the various embodiments can be used in
combination, or in substitution with each other as desired. That
one feature is not illustrated in all of the embodiments is not
meant to be construed that it cannot be so illustrated, but is done
for brevity of description. Thus, the various features of the
different embodiments can be mixed and matched as desired to form
new embodiments, whether or not the new embodiments are expressly
described. All combinations or permutations of features described
herein are covered by this disclosure.
[0041] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal languages of the claims.
* * * * *